A magnetic disk drive, such as a hard disk drive (HDD) comprises a magnetic recording medium, a spindle motor for spinning the magnetic recording medium, a head slider with a recording and reproducing element mounted thereon, a suspension for supporting the head slider, and a voice coil motor (VCM) to drive the suspension supporting the head slider such that the head slider is positioned where desired data is recorded.
The HDD, when recording and reproducing information, rotates the suspension with the VCM so that the recording and reproducing element (head element portion) flies above a desired track of the many tracks formed on the magnetic recording medium. The HDD locates the current position by retrieving a position signal called a servo signal arranged on the tracks and moves the recording and reproducing element to the desired track. In a recording operation, the HDD refers to a position signal retrieved by the reproducing element to move the recording element to the recording position. Similarly, in a reproducing operation, the HDD refers to the position signal retrieved by the reproducing element to move the reproducing element to the reproduction position.
Tracks are formed circumferentially, and as described above, the recording and reproducing element on a head slider moves by the VCM's rotational movement around the axis of the suspension. Accordingly, the angle between the recording element, the reproducing element, and the track vary with the radial position on the magnetic recording medium. The directional difference between the longitudinal direction of the head slider and the tangential direction (circumferential direction) of the track at the position of the recording element or the reproducing element is called a skew angle. The skew angle varies depending on the radial position of the magnetic recording medium.
As more and more requests for the digitalization of information and miniaturization of stored data have been made in recent years, higher recording density of magnetic recording medium is desired to accommodate these requests, particularly in HDDs. To attain such a high recording density, a recording area per bit should be reduced. However, this reduction causes the boundaries of recorded information (a recording bit) to not agree with the boundaries of magnetic particles. At the boundaries of recording bits, magnetic transition points are unstable, causing increases in noise. To suppress such noise, the diameters of magnetic particles may be reduced.
On the other hand, decreases in the particle diameter reduces magnetic energy of the magnetic particle and if the magnetic energy becomes lower than the thermal energy, evanescence of magnetic information, referred to as thermal fluctuation, occurs. To cope with the thermal fluctuations, the recording layer of a magnetic recording medium may be made of a magnetic particle material having a greater magnetic anisotropy constant. As a result, the coercivity increases together with the anisotropy, so the recording magnetic field has to be strengthened. To produce a stronger recording magnetic field, miniaturization of a recording element becomes difficult. Conversely, a recording magnetic field generated by a tiny recording element cannot exceed the coercivity of the magnetic recording medium, and information cannot be recorded.
To overcome the above-described problem, assisted magnetic recording schemes utilizing energy by heat or electromagnetic waves have been proposed. Among such schemes, heat-assisted magnetic recording (HAMR) is described with reference to FIG. 10. FIG. 10 indicates the relationship between the temperature and the coercivity of magnetic particles. The coercivity of a magnetic recording medium utilizing the magnetic particles is Hc0 at a normal temperature Tr° C. Warming the recording layer reduces the coercivity Hc. When the recording layer is heated to the temperature Tw or higher, the recording magnetic field Hw generated by a tiny recording element exceeds the Hc of the medium to allow recording. As a heating means, use of near-field light has been suggested in recent years, in addition to laser beams.
On the other hand, during non-recording, the temperature of the magnetic recording layer falls so that the coercivity returns to Hc0 at a high level. Thus, the high coercivity may provide the tolerance to thermal fluctuations during non-recording. In this way, the basic concept of HAMR is to reduce the coercivity of the recording layer by heating the magnetic recording medium and then to perform recording at the recording magnetic field intensity that the recording element is capable of generating. Such HAMR may be divided into the following three kinds in accordance with the coercivity of the recording layer of the magnetic recording medium and the recording magnetic field intensity from the head element portion, the kind and size of the constituent to heat the medium, and the like. In the present specification, these are referred to as the magnetic field scheme, the heat spot scheme, and the hybrid scheme.
FIG. 11A schematically depicts a configuration of the magnetic field scheme. An HDD according to the magnetic field scheme comprises a tiny recording element 602 compared with a wide heat spot (heating area) 601. The heat spot 601 is a demagnetization area. Data is recorded in the area where the heat spot 601 simultaneously overlaps with the recording magnetic field. In FIG. 11A, it is assumed that the recording magnetic field is formed in the area of the recording element 602. These are the same in the other figures which will be described later.
In FIG. 11A, the heat spot diameter is sufficiently larger than the width of the recording element. Hence, in the area where the recording magnetic field Hw is attained on the magnetic recording medium (the area where the heat spot 601 overlaps the recording element 602 in the drawing), the coercivity Hc of the magnetic recording medium is weaker than the magnetic intensity in the recording magnetic field Hw. Accordingly, the recording width (track width) on the magnetic recording medium is determined depending on the width of (the trailing edge of) the recording element 602. The recorded magnetization in the adjacent areas is not demagnetized by heat, or the effect of heat is minor.
FIG. 11B schematically depicts the configuration of the heat spot scheme. An HDD according to the heat spot scheme comprises a sufficiently wide recording element 604 compared with a narrower diameter of a heat spot 603. In this configuration, the area where the recording magnetic field Hw is attained on the magnetic recording medium (the area where the heat spot 603 overlaps the recording element 604 in the figure) has a width wider than the diameter of the heat spot 603. Data is recorded in the area where the heat spot 603 simultaneously overlaps with the recording magnetic field. Hence, the recording width (track width) is determined depending on the diameter of the heat spot 603. The recorded magnetization in the adjacent areas is not demagnetized by the recording magnetic field of the recording element 604, or the effect thereof is minor.
FIG. 11C schematically depicts the configuration of the hybrid scheme. Magnetic data is recorded in the area where the heat spot overlaps with the recording magnetic field. Namely, the width (recording width) 610 of the area where data has been recorded is that of the heat spot or of the recording magnetic field, whichever is smaller. In the present configuration, the magnetization of the magnetic recording layer is demagnetized not only by the heat within the heat spot but also by the recording magnetic field. Namely, the effect to the adjacent tracks reaches the area 611 where the heat spot diameter is wider or the area 612 where the recording magnetic field width is wider. Accordingly, it is necessary to design the heat spot diameter and the recording magnetic field width such that neither protrudes to the adjacent tracks.
A conventional technique, for example a technique disclosed in Japanese Patent Office Pub. No. 2007-12226, has been known that changes the heat spot diameter to attain a narrow track width independently of the heat spot diameter and the width of the recording element.
As described above, the width recorded in the HAMR is determined by the heat spot diameter and the width of the recording magnetic field. In a magnetic disk drive, like the above-described HDD, which employs a rotary actuator for moving a head slider by rotational movement of a VCM, the positional difference in the radial direction on a magnetic recording medium appears as change in positional difference in the radial direction of the elements on the head slider with change in skew angle. In other words, as the skew varies, the positions of the recording element and the assistance element vary in the radial direction. At a radial position having a great absolute value of the skew angle, the recording width varies unintentionally and disadvantageously. Accordingly, it would be advantageous to suppress variations in recording width even if the radial positions of an assistance element and a recording element vary due to the skew angle.